1. Field of the Invention
Embodiments of the present invention relate to an organic light emitting display and a driving method thereof. More particularly, embodiments relate to an organic light emitting display and a driving method thereof that are capable of calibrating a brightness change due to a deterioration of an organic light emitting diode and/or a temperature change.
2. Description of the Related Art
An organic light emitting display is a display that emits light by electrically exciting a fluorescent or phosphorescent organic compound and can display an image by driving N×M organic light emitting diodes.
An organic light emitting diode generally includes an anode (ITO), an organic thin-film, and a cathode (metal). The organic thin-film may be formed in a multi-layered structure including a light emitting layer, an electron transport layer ETL and a hole transport layer HTL. The organic thin-film may include a separate electron injecting layer EIL and a hole injecting layer HIL.
In general, in such an organic light emitting diode OLED, a voltage applied to an anode electrode is set to be higher than a voltage applied to a cathode electrode. Thus, carriers having negative polarity may accumulate on the anode electrode, and carriers having positive polarity may accumulate on the cathode electrode. If the carriers of negative polarity positioned on the anode electrode and the carriers of positive polarity positioned on the cathode electrode are maintained for a long time, movement of electron(s) and hole(s) contributing to light emission may be reduced. Thus, an average brightness may be lowered, i.e., lowering of brightness due to deterioration.
In general, an organic light emitting diode has characteristics of diode. Like other diodes, a current flowing through the organic light emitting diode and a voltage thereof may increase as the temperature increases. So, brightness of the organic light emitting diode may increase as the temperature increases. Thus, brightness calibration may be necessary, e.g., to lower the brightness. In particular, for a digital driving method, i.e., driving by a fixed voltage, the influence of a change in temperature on the operation of the organic light emitting diode may be more pronounced than for other driving methods.
In general, in organic light emitting displays, when an organic light emitting diode deteriorates, there may be variations in current efficiency variation and/or current-voltage characteristics. In particular, displays using a digital driving method, i.e., a method of driving by a constant voltage, may be significantly impacted by a current-voltage characteristic variation. That is, e.g., for displays employing a digital driving method, an extent and impact of a current-voltage characteristic variation may be larger. Furthermore, problems may arise when organic light emitting diodes are to have the same brightness, i.e., when a light emission current value flowing through the organic light emitting diode varies depending on an ambient temperature change, and thus brightness thereof also varies.
A method of displaying a specific pattern on a screen, measuring a current value at that time, and comparing the measured current value with an actual current value may be employed to calibrate for such a brightness variation. An element for measuring a current may be attached to an organic light emitting display module so as to measure a current. Accordingly, a cost and/or size of such an organic light emitting display may increase and/or it may not be possible to compare a current in real-time.